diff --git a/make/rules.mk b/make/rules.mk
index 7dbfa261..28709722 100644
--- a/make/rules.mk
+++ b/make/rules.mk
@@ -100,7 +100,7 @@ cvsupdate update:
 	if [ -d "CVS" ]; then cvs update -dP || exit 1; else git pull || exit 1; fi
 
 cvsdiff diff:
-	if [ -d "CVS" ]; then cvs diff -dP || exit 1; else git --no-pager diff || exit 1; fi
+	if [ -d "CVS" ]; then cvs diff -u || exit 1; else git --no-pager diff || exit 1; fi
 
 prepend_header:
 	set -e; for f in $(SRC_UNHEADERED); do sh $(TOPDIR)/hdr/prepend_header.sh $$f; done